Fossil fuel reserves are very restricted, and thus the depletion of the fossil fuel is inevitable. In particular, since main emission sources of greenhouse gas causing global warming are fossil fuels, advanced countries have been focused on developing hydrogen energy, and the like, using alternative energy or atomic energy so as to decrease fossil fuels. An example of energy sources which have emerged as alternative energy may include solar energy, wind power generation, hydrogen energy, biomass, and the like. To use solar power or wind power, auxiliary facilities, such as a solar panel and a windmill, are required. However, since a wide space is required to install the solar panel or the windmill, other environmental problems, such as destruction of ecosystem and noise, may occur. Future energy needs requirements, such as environmental acceptability, economic productibility, and eternal capability.
A fuel cell is a cell which directly converts chemical energy generated by oxidation into electrical energy and is a new eco-friendly future energy technology of generating electrical energy from materials, which richly exist on earth, such as hydrogen and oxygen.
The fuel cell performs an electrochemical reaction in an electrolysis reverse reaction type of water by supplying oxygen to a cathode and hydrogen to an anode to produce electricity, heat, and water, thereby generating electrical energy at high efficiency without inducing pollutants.
The fuel cell which produces electricity and heat using fuel such as city gas is a representative new growth engine industry which has a greenhouse gas reduction effect and a very large job creation effect, and therefore is positively being promoted and commercialized around the world.
The fuel cell may generate electricity and hot water and save light and heat expenses of homes, and contribute to global warming prevention.
A proton-exchange membrane fuel cell (PEMFC) is an environmentally-friendly energy technology for high energy conversion efficiency, load following capability, and energy deficiency due to emission of low pollutants. However, a residential power generator (RPG) using the typical PEMFC is vulnerable to carbon monoxide (CO) poisoning and is difficult to manage water, and therefore a balance of plant (BOP) is excessively required. Therefore, a system is large and initial cost is high. Further, the temperature of hot water supplied from the system is low and the availability of a heat source is reduced. As a method for solving the problem of the existing system, a high temperature PEMFC using a polybenzimidazole (PBI) membrane with which phosphoric acid is doped has been receiving attention. The technology does not use water but uses phosphoric acid, as transfer media of hydrogen ions, and has an operation temperature range between 120° C. and 190° C. Therefore, since external humidification is not required and water is created in a vapor phase on a cathode electrode layer, the technology may solve a complicated water management problem. The high operation temperature extremely increases poisoning resistance of a catalyst layer against pollutants such as CO and therefore a fuel reforming process may be simplified. Further, a stack temperature has a large temperature difference from external environment, such that cooling may be effectively performed, a high temperature heat source may be collected to increase heat availability, and performance and durability may be largely affected by operating conditions. Nevertheless, it is confirmed that a research period of the high temperature PEMFC is shorter than that of the typical PEMFC and therefore research cases of performance and durability depending on the operating conditions are very small and the operating conditions largely affect the performance and durability. However, the optimal operating conditions are not yet proposed.
Therefore, to maximize the performance and durability, a research for the optimization of the operating conditions has been required.
Korean Patent Laid-Open Publication No. 10-2011-0033490 discloses a method of operating a polymer electrolyte membrane fuel cell.